1. Field of the Invention
The present invention relates to an electric stringed instrument having means for detecting the vibration of a string by an electromagnetic pickup, e.g., an electric guitar, an electric bass guitar and an electric piano, and more particularly to an electric stringed instrument having a device that drives the string by an electromagnetic driver to sustain the vibration of the string detected by the electromagnetic pickup.
A guitar or a piano differs from a violin in that after the string of a guitar or a piano is excited, the magnitude of the vibration of the string will become half within about a half second and die within about 7 seconds. Particularly, for example, in the case of an electric guitar, it seems that attenuation speed of the vibration of the string is shorter than that of an acoustic guitar because of the electric characteristics of an amplifier. Thus, an effector, which is a device for adding several sound effects, i.e., Delay, Reverb, Compressor and Overdrive, etc. to the sound of the guitar is often used to enable more sustained sound to be heard acoustically.
The effector using the Delay or the Reverb adds reverberations to a musical sound, and the sound is produced by recording and playing back the sound on a magnetic tape or by delaying the tone by a spring arrangement. Recently, simple electronic devices using BBD (Bucket Brigade Device) have been utilized for the Delay or the Reverb. The effector using the Compressor increases the amplitude of a music signal by an amplifier in reverse proportion to attenuation characteristics of the vibration of the string, and the Overdrive amplifies the signal beyond a permissible level so as to obtain a long tone. A longer tone is available by using these effectors, although the effectors cannot maintain the tone after the vibration of the string has stopped.
Now, musicians investigate various sounds and develop the art of musical performance in order to play said various sounds in response to their individual artistic impression. For example, a style using a loudspeaker feedback is one that produces the sound of a guitar at high volume so as to sustain the vibration of the string on the guitar for a long time without attenuation by way of sympathetic vibration in cooperation with air vibration emitted from the loudspeaker. As described above, the feedback can maintain the vibration of the string for a long time, but in order to maintain the sound, the player must utilize a skilled and high-grade technique to overcome several limitations, i.e., a sound of volume, location of the amplifier, length of the strings and musical interval etc. Further, there is a weak point in that the tone of the first string on the treble side, which is most significant for musical expression, cannot be easily sustained. Therefore, a device that easily sustains the vibration of the string for an extended period is in demand.
2. Description of the Prior Art
Several prior arts disclose means for sustaining the vibration of the string in relation to an electric stringed instrument. For example, Patent KOKAI 52- 151022 and Utility Model KOKAI 53-139836 (Both applicants are Roland Ltd.) disclose such a type of an electric guitar such that the strings of the guitar are connected with an electric driving circuit mounted within the guitar, and a positive feedback current output from the circuit flows through the strings as a part of the circuit when detecting the vibration of the strings at a pickup on the guitar and then the strings, in which the positive feedback current is flowing, vibrate in cooperation with a magnet attached to a surface of the guitar. This type of guitar has no use of an electromagnetic driver that converts an electric signal into a magnetic driving force utilizing a variation of magnetic flux corresponding to the signal and drives the metal string by the driving force. Thus, the guitar has the advantage of having no generation of so-called "magnetic feedback" which is introduced by a leakage of flux fed back from the electromagnetic driver to an electromagnetic pickup. The electromagnetic pickup converts a variation of magnetic flux produced by the vibration of the metal string into an electric signal, but the guitar needs an outside powder supply to provide power for the self-driving strings. Further it must have a strong magnet to drive the strings, in which the positive feedback current flows, and also the system becomes large by connecting the strings to the circuit. Therefore, said type of electric guitar needs to be designed as an exclusive instrument, and consequentially it is not practical to manufacture it on a commercial basis.
Further, the other disclosure is described in Utility Model KOKAI 55-152597 (YAMAHA Ltd.). The pickup shown in the specification and the drawings uses a light-emitting element and a light-intercepting element, and thus, there is no need to consider the said magnetic feedback. However, this type of electric guitar does not use an electromagnetic pickup as described above so that a tone generated from said guitar is different from the tone of an electric guitar having a common electromagnetic pickup.
Furthermore, U.S. Pat. No. 4,941,388 (Hoover, et al.) discloses an arrangement that has an electromagnetic pickup and an electromagnetic driver in order to sustain vibration of the strings of an electric guitar without using the deformation type described above. The arrangement has an unbalancing device for putting the magnetic balance between the electromagnetic pickup and the electromagnetic driver out of balance so as to reduce the magnetic feedback, and as a particularly effective method, an embodiment using a shunting plate is disclosed. An electric guitar having a device for reducing the magnetic feedback by using the shunting plate is put into practical use and a device by the name of "Sustaniac" is available on the market. However, even if the shunting plate is used, a part of the magnetic feedback that cannot be completely absorbed into the shunting plate remains. In order to reduce the magnetic flux from the electromagnetic driver to the electromagnetic pickup as much as possible, the design of the shunting plate is limited to match magnetic characteristics precisely and an orientating winding pole pieces of the electromagnetic pickup and the electromagnetic driver, and further the shunting plate needs to utilize the only so-called hum-bucking pickup.